1. Field of the Invention
The present invention relates to a robot arm mechanism having arms contracted and extended, and more particularly to a robot arm mechanism incorporating an arm driving mechanism for driving the arms to assume its contracted and extended positions.
2. Description of the Related Art
The robot arm mechanism of this type is used in the process of producing semiconductors in which the robot arm mechanism is operated to have arms contracted and extended to handle works, i.e., objects to be treated. These objects include for example such as wafers and other precision parts that are to be transferred and then unloaded onto a work table by the robot arm mechanism.
A conventional robot arm mechanism of this kind is disclosed in, for example, Japanese patent No.2808826 and comprises a handle member for holding and releasing objects, and robot arms for operating and moving the hand. The robot arms are constituted by a plurality of parallel links having pivotable joint portions on which are provided synchronous gears for maintaining the links in their parallel attitudes. The synchronous gears are rotated to have the hand maintained in its predetermined direction by moving the hand forwardly and rearwardly while the parallel links are operated. The parallel links are pivotably supported at their base portions by a rotating disc and driven to be contacted and extended by two electric motors through couplings and transfer shafts. The rotating disc is formed gear teeth around its side to mesh with a drive gear driven by another electric motor so as to rotate the robot arms.
Another conventional robot arm mechanism of this kind is disclosed in Japanese patent laying-open publication Tokkaihei 10-156770 and comprises robot arms constituted by a plurality of parallel links to form a first parallelogram linkage contractable and extensible, and a synchronous motion mechanism including gears, belts and pulleys operatively mounted on the links. The synchronous motion mechanism is operated to have gears, belts and pulleys driven so that the first parallelogram linkage can be contracted and extended. The parallel links are supported by a rotating disk and connected with a second parallelogram linkage driven by a first electric motor through a driving arm pivotably connected to the second parallelogram linkage to contract and extend the first parallelogram linkage. The first electric motor is positioned away from a rotation axis of the rotating disk. The rotating disk is driven by a second electric motor so as to rotate the robot arms.
A third conventional robot arm mechanism of this kind is disclosed in Japanese patent laying-open publication Tokkaihei 07-73833 and comprises robot arms constituted by four pivotably connected links to form a diamond-shaped linkage contractable and extensible, and a synchronous motion mechanism including gears, belts and pulleys operatively mounted on the links. The synchronous motion mechanism is operated to have gears, belts and pulleys driven so that the diamond-shaped linkage can be contracted and extended. The links has a pair of handling members and are pivotably connected to two driving arms supported by a center hub. The arms are driven clockwise or counterclockwise independently of each other around a rotation axis by two electric motors, which enable the diamond-shaped linkage to be contracted and extended.
The above known conventional robot arm mechanisms, however, encounter such problems as follows;
The above known first conventional robot arm mechanism requires three electric motors; two motors to drive the links for the purpose for contracting and extending the robot arms and one motor to drive the rotating disk for the purpose of rotating the robot arms, resulting in larger size and higher cost.
The above known second conventional robot arm mechanism has a limit of a rotation angle of the robot arms, for the electric motor for contracting and extending the arms has to be arranged away from the rotation axis of the rotating disk and moved around it. To avoid the above limit of rotation, it takes a high cost and a complex structure, for such a device as brush electric contact mechanism has to be added.
The above known third conventional robot arm mechanism has such a problem that the diamond-shaped linkage can not bring the handling members beyond the rotation axis and is equipped with such long links that they may interfere other parts of the robot arm mechanism.
It is, therefore, an object of the present invention to provide a robot arm mechanism which overcomes the foregoing drawbacks and can drive the robot arms to assume its contracted and extended positions and to rotate without a limit of a rotation angle by only two motors.
It is another object of the present invention to provide a robot arm mechanism with a simple construction.
According to the first aspect of the present invention there is provided a robot arm mechanism comprising: a plurality of handling members for supporting and handling an object, the plurality of handling members comprising a first handling member and a second handling member, a robot arm connected to the handling members, the robot arm comprising a first arm link having first and second end portions and a first pivotable joint portion between the first and second end portions of the first arm link, a second arm link having first and second end portions and a first pivotable joint portion between the first and second end portions of the second arm link, the first and second arm links respectively rotatable around a rotation axis, a link retaining mechanism for retaining attitudes of the first and second handling members, a link operating mechanism for operating the link retaining mechanism according to a rotation angle between the first and second arm links, the link operating mechanism comprising a lever member pivotably connected with the link retaining mechanism, the lever member comprising a crank and a coupling link respectively having first and second end portions, the crank pivotably connected at the first end of the crank with one of the first and second arm links, the crank integrally connected to the coupling link, the link operating mechanism further comprising a connecting link having first and second end portions, the connecting link pivotably connected at the first end portion of the connecting link to the other of the first and second arm links, the connecting link and the coupling link pivotably connected with each other at the second end portion of the connecting link and the second end portion of the coupling link, a robot arm driving mechanism for driving the robot arm, the robot arm driving mechanism comprising a first driving shaft and a second driving shaft.